Preferences vary from culture to culture, and people crave what they don't have. While many curvy women strive to be stick-thin, those with flat derrieres often desire more lift and roundness. This effect can be accomplished through exercise, cosmetic procedures or even a commercially available fanny lifter. You can make your own fanny lifter with little effort or expense.
Fully loosen the straps on your bra.
Cut off the straps from your bra. Take care not to cut into the looped ends, since you will need to adjust the straps later. Cut into the plastic loop that attaches these ends of the straps to remove the straps without damaging the loop.
Put on the bikini underpants. Hold one end of the bra strap to the crotch portion of the underpants. Hold the other end of the bra strap to the portion of the elastic waistband that hits your side. Mark these two portions of the underpants so you can sew the bra straps on. Repeat on the other side.
Remove the underpants and sew the bra straps where you made these markings. Sew with the slider (adjuster) facing out so that it doesn't press against your leg, and also to make it easier to adjust.
Put the underpants back on. Place the bra straps under your buttocks and adjust the bra straps to create lift.